JP2000054890A - Fuel injection control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform a sure fuel injection by controlling the fuel pressure to be supplied to a solenoid fuel injection valve to a target fuel pressure according to engine operating state, and reducing the target fuel pressure when the engine temperature is high. SOLUTION: In normal starting of an engine, the actual fuel pressure within an accumulation chamber 2 is set substantially to the atmospheric pressure, and the target fuel pressure is set to a first target fuel pressure when the engine temperature is sufficiently low. When the difference between the first target fuel pressure and the actual fuel pressure is a prescribed value or more, and the cooling water temperature is a prescribed value or higher, a second target fuel pressure lower than the first target fuel pressure is set to execute the maximum discharge operation of a high-pressure pump 7. At that time, the fuel pressure to be supplied to a fuel injection valve 1 is controlled to the target fuel pressure according to the engine operation state, and the target fuel pressure is reduced when the engine temperature is high. Accordingly, a sure fuel injection can be performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a fuel injection control device for an internal combustion engine.

[0002]

2. Description of the Related Art In order to directly inject high-pressure fuel into a cylinder, a high-pressure fuel is stored in a pressure-accumulation chamber, and the fuel in the pressure-accumulation chamber is injected through a fuel injection valve arranged for each cylinder. A known fuel injection device is known. A fuel injection valve used in this fuel injection device is generally of an electromagnetic type, and a valve element urged in a valve closing direction by a spring force and a fuel pressure is opened by suction by a solenoid. is there.

[0003] As the temperature of the coil of the solenoid increases, the current-carrying resistance increases, so that the attraction force of the solenoid decreases. The fuel pressure in the accumulator is controlled by a fuel pump to be near a predetermined high fuel pressure. The solenoid has a sufficiently large suction force so that even if the suction force of the solenoid decreases at a high temperature of the engine, the valve can be opened by sucking the valve body on which the spring force and the fuel pressure near the predetermined high fuel pressure act. It is assumed to have.

[0004]

When the engine is started,
The fuel pressure in the accumulator must be increased from the atmospheric pressure to a predetermined high fuel pressure at an early stage. For this purpose, a maximum discharge operation of the fuel pump is performed. This maximum discharge amount operation is switched to a normal operation according to the fuel injection amount when the fuel pressure in the accumulator reaches a predetermined high fuel pressure.
The output of the fuel pump does not change instantaneously,
In addition, due to the influence of control response delay, etc., the fuel pressure in the accumulator continues to rise and may relatively exceed a predetermined high fuel pressure.

[0005] At this time, if the engine temperature is not so high, it is possible to open the valve element on which the fuel pressure relatively larger than the predetermined high fuel pressure acts by a sufficiently large suction force of the solenoid. However, for example,
In the case of restart immediately after high-speed, high-load operation, if the suction force of the solenoid is reduced due to the extremely high engine temperature, and the fuel pressure in the accumulator significantly exceeds the predetermined high fuel pressure, this The valve body on which the fuel pressure acts cannot be opened, and there is a possibility that the engine is stopped without fuel being injected.

Japanese Patent Application Laid-Open No. 9-195819 discloses that the target fuel pressure in the accumulator is controlled according to the engine load and the engine speed, but such control solves the above-mentioned problem. I can't. Further, it is conceivable to further increase the suction force of the solenoid, but it is difficult to arrange the solenoid in the fuel injection valve with the increase in size of the solenoid.

Accordingly, an object of the present invention is to provide an electromagnetic fuel injection valve having a valve body in which the fuel pressure acts in a valve closing direction, without increasing the size of a solenoid for opening the valve body, without increasing the engine temperature. An object of the present invention is to provide a fuel injection control device for an internal combustion engine that enables reliable fuel injection even at times.

[0008]

According to a first aspect of the present invention, there is provided a fuel injection control device for an internal combustion engine, wherein a valve body in which fuel pressure acts in a valve closing direction and a solenoid for sucking the valve body in a valve opening direction. An electromagnetic fuel injection valve having: a target fuel pressure control means for controlling a fuel pressure supplied to the electromagnetic fuel injection valve to a target fuel pressure corresponding to an engine operating state; and reducing the target fuel pressure when the engine temperature is high. Target fuel pressure changing means.

A fuel injection control device for an internal combustion engine according to a second aspect of the present invention is the fuel injection control device for an internal combustion engine according to the first aspect, wherein the target fuel pressure changing means includes:
It is characterized in that the target fuel pressure is changed based on the map.

[0010]

FIG. 1 is a schematic diagram showing an embodiment of a fuel injection control device for an internal combustion engine according to the present invention. Although the internal combustion engine in the present embodiment will be described below as having four cylinders, this does not limit the present invention. FIG.
In the drawings, reference numeral 1 denotes four fuel injection valves arranged for each cylinder, and reference numeral 2 denotes a pressure accumulation chamber for supplying high-pressure fuel to each fuel injection valve 1. The fuel injection valve 1 has a valve element for opening and closing the injection hole, and a solenoid for sucking the valve element in the valve opening direction. The spring force and the fuel pressure in the pressure accumulating chamber 2 act on the valve body in the valve closing direction. When the solenoid is demagnetized, reliable valve closing is compensated and fuel injection is stopped.
When the solenoid is excited, the solenoid attracts the valve body in the valve opening direction against the spring force and the fuel pressure, and fuel injection is performed.

Reference numeral 3 denotes a fuel tank, in which a low-pressure pump 4 is disposed. The low-pressure pump 4 is an electric pump driven by a battery.
It has a rated discharge pressure of 0.3 MPa. The low-pressure pump 4 is activated simultaneously with the ON signal of the starter switch. Reference numeral 6 denotes a filter for removing foreign matter from the fuel sucked by the low-pressure pump 4.

Reference numeral 7 designates a pressure accumulating chamber 2 having, for example,
This is a high-pressure pump for raising the pressure to near a predetermined high fuel pressure of MPa. The high-pressure pump 7 has a plunger 7a slidable in a cylinder. The space 7d in the cylinder of the high-pressure pump 7 having the suction side opening 7b and the discharge side opening 7c serves as a pump chamber. The sliding operation of the plunger 7a for narrowing the pump chamber 7d, that is, the discharge stroke operation of the plunger 7a is provided by the cam 7e connected to the crankshaft of the engine body, and the sliding operation of the plunger 7a for expanding the pump chamber 7d. That is, the plunger 7a
Is performed by the compression spring 7f.
In the present embodiment, the cam 7e provides two discharge strokes in one rotation. However, the cam 7e is provided via a reduction gear or the like so that two rotations of the cam 7e correspond to one rotation of the crankshaft. Connected to the crankshaft,
That is, a discharge stroke of the high-pressure pump 7 is provided every time fuel is injected into the two cylinders.

The suction opening 7b of the pump chamber 7d communicates with the control chamber 7g. The control chamber 7 g is connected on the one hand to the discharge side of the low-pressure pump 4 by a suction pipe 8 and on the other hand to the fuel tank 3 by a return pipe 9.
A filter 10 for removing foreign matter from fuel discharged from the low-pressure pump 4 is disposed in the suction pipe 8.

The discharge side opening 7c of the pump chamber 7d is connected to the accumulator 2 by a discharge pipe 11. The discharge pipe 11 is provided with a check valve 12 that allows only the fuel flow toward the accumulator 2. The check valve 12 is opened even by a slight pressure difference.

A first relief valve 13 that allows only the fuel flow toward the fuel tank 3 is disposed in the return pipe 9, and is connected to the accumulator chamber 2 by a connection pipe 14 on the downstream side of the first relief valve 13. I have. Connection pipe 14
, A second relief valve 15 that allows only the fuel flow from the accumulator 2 is disposed. The first relief valve 13 opens at a pressure slightly larger than the rated discharge pressure of the low-pressure pump 4. Second relief valve 15
The valve opens when the pressure in the accumulator 2 reaches a predetermined pressure higher than the predetermined high fuel pressure, and prevents the fuel pressure in the accumulator 2 from becoming abnormally high.

Reference numeral 16 denotes a solenoid valve for opening and closing the suction side opening 7b of the high-pressure pump 7. The electromagnetic valve 16 is closed by exciting the electromagnetic solenoid 16a, and is opened by a spring 16b by demagnetizing the electromagnetic solenoid 16a. The solenoid valve 16 is opened during the suction stroke of the high-pressure pump 7 and is closed for a required time during the discharge stroke. Thereby, during the suction stroke of the high-pressure pump 7,
Fuel discharged from the low-pressure pump 4 is sucked into the pump chamber 7d,
During closing of the solenoid valve 16 in the discharge stroke, the discharge pipe 11 is closed.
The fuel in the pump chamber 7d is pumped to the pressure accumulating chamber 2 via
On the other hand, during opening of the solenoid valve 16 in the discharge stroke,
When the fuel pressure in the accumulator 2 is higher than the opening pressure of the first relief valve 13, the fuel in the pump chamber 7 d is returned to the return pipe 9.
When the fuel pressure in the accumulator 2 is lower than the opening pressure of the first relief valve 13, the fuel in the pump chamber 7 d is pumped to the accumulator 2 via the discharge passage 11. Is done.

In the solenoid coil of the fuel injection valve 1, the higher the temperature is, the higher the current-carrying resistance is, and the lower the attraction force of the solenoid is. As a result, the solenoid of the fuel injection valve 1 can sufficiently open the valve by attracting the valve body on which the spring force and the predetermined high fuel pressure acts even if the suction force of the solenoid decreases at a high engine temperature. It has a large suction force.

A control device 20 controls the opening and closing of the electromagnetic valve 16 via the electromagnetic solenoid 16a. The control device 20 detects a fuel pressure in the accumulator 2 and an engine operating state. (Not shown) such as an air flow meter, a rotation sensor, and a cooling water temperature sensor.

FIG. 2 shows the high-pressure pump 7 by the control device 20.
3 is a flowchart for opening / closing control of the electromagnetic valve 16 of FIG. This flowchart is executed simultaneously with the ON signal of the starter switch, and is repeated every predetermined time. First, in step 101, the pressure sensor 21
Thus, the actual fuel pressure P in the accumulator 2 is measured. Next, at step 102, the difference dP between the first target fuel pressure P1 set at the predetermined high fuel pressure and the actual fuel pressure P is calculated, and the routine proceeds to step 103.

In step 103, it is determined whether or not the difference dP is equal to or greater than a predetermined value dP '. When this determination is denied, the actual fuel pressure P becomes the first target fuel pressure P
This is a value relatively close to 1. At this time, step 104
In, the target fuel pressure Pt is set to the first target fuel pressure P1. Next, in step 105, the valve closing time of the solenoid valve 16 during the discharge stroke of the high-pressure pump 7 is obtained by adding the pressure compensation fuel amount for reducing the difference dP to the current fuel injection amount injected by the fuel injection valve 1. Control is performed so that only the fuel amount is discharged. Here, when the difference dP is a negative value, that is, when the actual fuel pressure P exceeds the first target fuel pressure P, the pressure compensation fuel amount becomes a negative value and is subtracted from the current fuel injection amount. You.

In this flowchart, the amount of pressure compensation fuel is set to be relatively small. Thereby, several times of discharge of the high-pressure pump 7 may be required until the actual fuel pressure P substantially matches the first target fuel pressure P1.
Since the current difference dP between the first target fuel pressure P1 and the actual fuel pressure P is relatively small, there is no problem in controlling the fuel injection amount by slightly correcting the opening time of the fuel injection valve. . In this manner, the actual fuel pressure P is reduced to the first target fuel pressure P by the relatively small pressure compensation fuel amount.
It can be prevented that the value fluctuates largely around 1. Of course, the pressure compensation fuel amount may be changed according to the magnitude of the difference dP.

On the other hand, when the determination in step 103 is affirmative, that is, when the difference dP between the first target fuel pressure P1 and the actual fuel pressure P is equal to or more than a predetermined value dP ', and the actual fuel pressure P When the pressure is significantly lower than the pressure P1, the routine proceeds to step 106, where it is determined whether or not the actual cooling water temperature THW measured by the cooling water temperature sensor is equal to or higher than a predetermined value THW '. When this judgment is denied, for example,
As at the time of normal engine start, the actual fuel pressure P
Is approximately atmospheric pressure, and when the engine temperature is sufficiently low, the routine proceeds to step 107, where the target fuel pressure Pt is set to the first target fuel pressure P1.

Next, the routine proceeds to step 109, where the solenoid valve 16 is closed over the entire discharge stroke of the high-pressure pump 7, and the high-pressure pump 7 is operated at the maximum discharge rate. That is, all the discharged fuel amounts other than those used for the fuel injection are regarded as the pressure-compensating fuel amounts. At this time, since the current difference dP between the first target fuel pressure P1 and the actual fuel pressure P is relatively large, the intended fuel amount may not be injected even if the valve opening time of the fuel injection valve is corrected. , Actual fuel pressure P
Needs to be approximately equal to the first target fuel pressure P1 at an early stage. Thereby, the pressure compensation fuel amount is set to be large.

Next, at step 110, the pressure accumulating chamber 2
The actual fuel pressure P is measured again, and it is determined in step 111 whether the actual fuel pressure P has reached the target fuel pressure Pt, that is, the first target fuel pressure P1. When this determination is denied, the process returns to step 109, and the maximum discharge amount operation of the high-pressure pump 7 is continued.

Thus, the actual fuel pressure P becomes equal to the target fuel pressure P
When t is reached, the processing from step 101 is performed,
At this time, since the determination in step 103 is denied, the control of the high-pressure pump 7 in step 105 is performed. That is, when the actual fuel pressure P reaches the first target fuel pressure P1, the maximum discharge amount operation of the high-pressure pump 7 is stopped, but the actual fuel pressure P in the accumulator 2 is reduced due to a response delay. As shown by the dotted line in FIG.
1 will be greatly exceeded.

However, at present, the actual cooling water temperature T
Since the HW is relatively low and the suction force of the solenoid in the fuel injection valve 1 is sufficiently high, the first predetermined fuel pressure PH which is much higher than the first target fuel pressure P1 (predetermined high fuel pressure) acts on the valve body. Even if it does, the valve body can be opened.
Thus, even if the fuel pressure P in the accumulator 2 greatly exceeds the first target fuel pressure P1, fuel injection can be performed without any problem.

On the other hand, if the actual cooling water temperature THW is relatively high, the suction force of the solenoid in the fuel injection valve 1 decreases, so that it is higher than the first target fuel pressure P1 but close to the first target fuel pressure P1. The valve can be opened only when the fuel pressure equal to or lower than the second predetermined fuel pressure PL is acting on the valve.

As a result, when the difference dP between the first target fuel pressure P1 and the actual fuel pressure P is equal to or more than the predetermined value dP ', the actual cooling water temperature T
When the HW is equal to or higher than the predetermined value THW ', for example, when the engine is restarted immediately after a high-speed, high-load operation, the actual fuel pressure P in the accumulator 2 is almost atmospheric pressure and the engine temperature is relatively high. At the time, when the maximum discharge amount operation of the high-pressure pump 7 is performed up to the first target fuel pressure P1, the fuel pressure P in the accumulator 2 greatly increases the first target fuel pressure P1 as shown by a dotted line in FIG. Exceeding the second predetermined fuel pressure PL, the valve element cannot be opened by the solenoid. Thus, the engine is stopped without fuel being injected.

In this flowchart, when the difference dP between the first target fuel pressure P1 and the actual fuel pressure P is equal to or higher than the predetermined value dP 'and the actual cooling water temperature THW is equal to or higher than the predetermined value THW', the determination in step 106 is affirmed. Step 108
The target fuel pressure Pt is set to the second target fuel pressure P2 lower than the first target fuel pressure P1, and in step 109, the maximum discharge amount operation of the high-pressure pump 7 is performed.

Thus, at step 111, when the actual fuel pressure P reaches the second target fuel pressure P2, the maximum discharge operation of the high-pressure pump 7 is stopped. The control of the high-pressure pump 7 using the fuel amount is performed.

Thus, the actual fuel pressure P in the accumulator 2 becomes
As shown by the solid line in FIG. 4, immediately after the high-pressure pump 7 stops operating, the second target fuel pressure P2
However, the valve does not exceed the second predetermined pressure PL, and the valve body can be reliably opened even by the solenoid having a reduced suction force, and the engine stops without fuel injection. Can be prevented.

FIG. 3 is a map for determining the target fuel pressure based on the cooling water temperature THW and the difference dP between the predetermined high fuel pressure and the actual fuel pressure. By using such a map, the above-described flowchart can be simplified.

In this flowchart, the difference d between the cooling water temperature as the engine temperature and the predetermined high fuel pressure and the actual fuel pressure.
Although the two target fuel pressures are selectively used in accordance with P, this does not limit the present invention, and three or more target fuel pressures may be selectively used based on the same concept. In the present flowchart, the target fuel pressure may be changed according to the engine operating state.

[0034]

As described above, according to the fuel injection control apparatus for an internal combustion engine according to the present invention, the electromagnetic fuel having the valve element in which the fuel pressure acts in the valve closing direction and the solenoid for sucking the valve element in the valve opening direction. An injection valve, and target fuel pressure control means for controlling the fuel pressure supplied to the electromagnetic fuel injection valve to a target fuel pressure corresponding to the engine operating state, wherein the target fuel pressure changing means reduces the solenoid attraction force. In order to lower the target fuel pressure when the engine temperature is high, even if the fuel pressure supplied to the fuel injection valve greatly exceeds the target fuel pressure due to response delay, etc. It does not rise. Thereby, without enlarging the solenoid to further increase the suction force of the solenoid,
Reliable fuel injection is possible even at high engine temperatures.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an embodiment of a fuel injection control device for an internal combustion engine according to the present invention.

FIG. 2 is a flowchart for opening / closing control of a solenoid valve of a high-pressure pump.

FIG. 3 is a map showing a relationship between a first target fuel pressure and a second target fuel pressure.

FIG. 4 is a time chart showing a change in actual fuel pressure in a pressure storage chamber.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Fuel injection valve 2 ... Pressure accumulation chamber 3 ... Fuel tank 4 ... Low pressure pump 7 ... High pressure pump 16 ... Solenoid valve 20 ... Control device

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02M 51/00 F02M 51/00 F 55/02 350 55/02 350E

Claims (2)

[Claims] 1. An electromagnetic fuel injection valve having a valve body in which fuel pressure acts in a valve closing direction, a solenoid for attracting the valve body in a valve opening direction, and an engine for supplying fuel pressure to the electromagnetic fuel injection valve. A fuel injection control device for an internal combustion engine, comprising: target fuel pressure control means for controlling a target fuel pressure according to an operating state; and target fuel pressure changing means for reducing the target fuel pressure when the engine is at a high temperature. . 2. The fuel injection control device for an internal combustion engine according to claim 1, wherein the target fuel pressure changing means changes the target fuel pressure based on a map.